Central Active Galactic Nuclei (central + active_galactic_nucleus)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Feedback under the microscope , I. Thermodynamic structure and AGN-driven shocks in M87

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2010
E. T. Million
ABSTRACT We present the first in a series of papers discussing the thermodynamic properties of M87 and the central regions of the Virgo Cluster in unprecedented detail. Using a deep Chandra exposure (574 ks), we present high-resolution thermodynamic maps created from the spectra of ,16 000 independent regions, each with ,1000 net counts. The excellent spatial resolution of the thermodynamic maps reveals the dramatic and complex temperature, pressure, entropy and metallicity structure of the system. The ,X-ray arms', driven outwards from M87 by the central active galactic nuclei (AGN), are prominent in the brightness, temperature and entropy maps. Excluding the ,X-ray arms', the diffuse cluster gas at a given radius is strikingly isothermal. This suggests either that the ambient cluster gas, beyond the arms, remains relatively undisturbed by AGN uplift or that conduction in the intracluster medium (ICM) is efficient along azimuthal directions, as expected under action of the heat-flux-driven buoyancy instability (HBI). We confirm the presence of a thick (,40 arcsec or ,3 kpc) ring of high-pressure gas at a radius of ,180 arcsec (,14 kpc) from the central AGN. We verify that this feature is associated with a classical shock front, with an average Mach number M= 1.25. Another, younger shock-like feature is observed at a radius of ,40 arcsec (,3 kpc) surrounding the central AGN, with an estimated Mach number M, 1.2. As shown previously, if repeated shocks occur every ,10 Myr, as suggested by these observations, then AGN-driven weak shocks could produce enough energy to offset radiative cooling of the ICM. A high significance enhancement of Fe abundance is observed at radii 350,400 arcsec (27,31 kpc). This ridge is likely formed in the wake of the rising bubbles filled with radio-emitting plasma that drag cool, metal-rich gas out of the central galaxy. We estimate that at least ,1.0 × 106 solar masses of Fe has been lifted and deposited at a radius of 350,400 arcsec; approximately the same mass of Fe is measured in the X-ray bright arms, suggesting that a single generation of buoyant radio bubbles may be responsible for the observed Fe excess at 350,400 arcsec. [source]

Swimming against the current: simulations of central AGN evolution in dynamic galaxy clusters

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2010
Brian J. Morsony
ABSTRACT We present a series of three-dimensional hydrodynamical simulations of central active galactic nuclei (AGN)-driven jets in a dynamic, cosmologically evolved galaxy cluster. Extending previous work, we study jet powers ranging from Ljet= 1044 erg s,1 to Ljet= 1046 erg s,1 and in duration from 30 to 200 Myr. We find that large-scale motions of cluster gas disrupt the AGN jets, causing energy to be distributed throughout the centre of the cluster, rather than confined to a narrow angle around the jet axis. Disruption of the jet also leads to the appearance of multiple disconnected X-ray bubbles from a long-duration AGN with a constant luminosity. This implies that observations of multiple bubbles in a cluster are not necessarily an expression of the AGN duty cycle. We find that the ,sphere of influence' of the AGN, the radial scale within which the cluster is strongly affected by the jet, scales as R,L1/3jet. Increasing the duration of AGN activity does not increase the radius affected by the AGN significantly, but does change the magnitude of the AGN's effects. How an AGN delivers energy to a cluster will determine where that energy is deposited: a high luminosity is needed to heat material outside the core of the cluster, while a low-luminosity, long-duration AGN is more efficient at heating the inner few tens of kpc. [source]

Quenching cluster cooling flows with recurrent hot plasma bubbles

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2004
Claudio Dalla Vecchia
ABSTRACT The observed cooling rate of hot gas in clusters is much lower than that inferred from the gas density profiles. This suggests that the gas is being heated by some source. We use an adaptive-mesh refinement code (flash) to simulate the effect of multiple, randomly positioned, injections of thermal energy within 50 kpc of the centre of an initially isothermal cluster with mass M200= 3 × 1014 M, and kT= 3.1 keV. We have performed eight simulations with spherical bubbles of energy generated every 108 yr, over a total of 1.5 Gyr. Each bubble is created by injecting thermal energy steadily for 107 yr; the total energy of each bubble lies in the range (0.1,3) ×1060 erg, depending on the simulation. We find that 2 × 1060 erg per bubble (corresponding to an average power of 6.3 × 1044 erg s,1) effectively balances energy loss in the cluster and prevents the accumulation of gas below kT= 1 keV from exceeding the observational limits. This injection rate is comparable to the radiated luminosity of the cluster, and the required energy and periodic time-scale of events are consistent with observations of bubbles produced by central active galactic nuclei in clusters. The effectiveness of this process depends primarily on the total amount of injected energy and the initial location of the bubbles, but is relatively insensitive to the exact duty cycle of events. [source]

Effect of turbulent diffusion on iron abundance profiles

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006
P. Rebusco
ABSTRACT We compare the observed peaked iron abundance profiles for a small sample of groups and clusters with the predictions of a simple model involving the metal ejection from the brightest galaxy and the subsequent diffusion of metals by stochastic gas motions. Extending the analysis of Rebusco et al., we found that for five out of eight objects in the sample an effective diffusion coefficient of the order of 1029 cm2 s,1 is needed. For AWM4, Centaurus and AWM7 the results are different suggesting substantial intermittence in the process of metal spreading across the cluster. There is no obvious dependence of the diffusion coefficient on the mass of the system. We also estimated the characteristic velocities and the spatial scales of the gas motions needed to balance the cooling losses by the dissipation of the same gas motions. A comparison of the derived spatial scales and the sizes of observed radio bubbles inflated in the ICM by a central active galactic nucleus (AGN) suggests that the AGN/ICM interaction makes an important (if not a dominant) contribution to the gas motions in the cluster cores. [source]

Isothermal shocks in Abell 2199 and 2A 0335+096?

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2006
J. S. Sanders
ABSTRACT We report on a partially circular X-ray surface brightness discontinuity found at about 55 kpc from the centre of Abell 2199 with Chandra X-ray Observatory observations. Unlike cold fronts found in other clusters, the feature shows no significant temperature change across it but has an apparent density jump. We therefore identify it as a weak isothermal shock associated with the central active galactic nucleus and the inflation of its radio bubbles, as found in the Perseus cluster. We examine a similar feature at 40 kpc radius found by Mazzotta et al. in 2A 0335+096, and conclude that it too may be an isothermal shock. The change in density if these are shocks implies a Mach number of ,1.5. If the isothermal nature of these features is confirmed by deeper observations, the implication is that such shocks are common in clusters of galaxies, and are an important mechanism for the transport of energy from a central supermassive black hole into the cluster core. [source]